Recent experiments have suggested that conjugation of 5-hydroxytryptamine, dopamine and norepinephrine plays a role in the inactivation of these amines at synapses in the central nervous system and, in some circumstances, at peripheral neuroeffector junctions. Studies are proposed to determine whether these conjugates are sulfates or glucuronides. In addition, it is proposed to determine the importance of conjugation relative to reactions catalyzed by monoamine oxidase and catechol methyltransferase (for catecholamines) in the inactivation of these amines. Superfused slices of brain regions specifically rich in 5-hydroxytryptamine terminals, dopamine terminals, or norepinephrine terminals will be used in these studies, and, in addition, ventriculocisternal perfusions of brain. Concentrations of amines and their metabolites will be measured in superfusates and in tissue extracts using liquid chromatography with electrochemical detection. Initial experiments will involve the comparison of the importance of conjugation in four species (rat, cat, dog, and rabbit). The species that is most efficient at conjugation will then be used for the rest of the studies, since conjugation appears to be important in human brain. Amines and their metabolites will be measured in superfusates and in slices under basal conditions, during release of transmitter evoked by direct and indirect mechanisms, during inhibition of monamine oxidase or catechol methyltransferase, and during administration of amino acid precursors (5-hydroxytryptophan or 3,4-dihydroxyphenylalanine).